Publication Nos. DE 25 05 585 C3; DE 36 25 795 C2; and DE 35 30 776 C2, describe a scale that is used to detect the relative location of a movable part of a machine tool. In this example, the scale is secured as part of a measuring instrument to the machine bed of the machine. To detect the relative location of the machine bed and a workpiece clamped onto it with respect to a tool disposed on a movable part of the machine, a scanning unit is attached to the movable part of the machine, for example. Thus, the scanning unit is secured to the movable part of the machine and scans the scale which is attached to the fixed machine bed. For securing the scale to an object it is known from German Patent Publication No. DE 25 05 585 C3 (corresponding to U.S. Pat. No. 4,070,759) to introduce the scale into a hollow body that is secured to the object by a jointlike fastening elements provided on its ends. This arrangement avoids constraining forces in attaching the hollow body in which the scale is received.
Along with the incidence of constraining forces in attaching a scale, or the housing of a scale, the change in length of the components as a result of temperature fluctuations causes particular problems. German Patent Publication No. DE 36 25 795 C2 (corresponding to U.S. Pat. No. 4,776,098) disclosed that it was possible to adjust the location of a measurement reference point on the scale independently of particular conditions of the processing machine to which the scale is attached, and in particular with regard to the temperature behavior. To that end, various length compensating elements are provided.
Ideally, however, the scale should be secured to an object in such a way that its expansion behavior in response to temperature fluctuations is adapted to the expansion behavior of the object to which it is attached. In order to assure that a scale attached to an object will "breathe" along with the object, or, in other words, will adapt itself in terms of its longitudinal expansion and shrinkage to the behavior of the object, scales of measuring instruments known in the art are secured by correspondingly strong screws. That is, in such a connection, the scale is pressed against the object with such force that it follows the lengthwise changes of the object because of the forces of friction transmitted to a contact-pressure face.
However, such a connection makes high demands of the fastening screws to be used and moreover cannot guarantee that the longitudinal expansion of the scale will be uniform over its entire length. Moreover, particularly with long scales, vibration can occur that causes measurement errors in detecting the relative location of the object to which the scale is secured. These problems exist equally with regard to the attachment of the scanning unit that cooperates with the scale.
In the arrangement described in German Patent Publication No. DE 35 30 776 C2 (corresponding to U.S. Pat. No. 4,649,648), an interlocking/form fitting connection of the scale to an object is provided. This interlocking connection is affected by rounded surfaces of elements provided on the scale and mounting blocks that are to be attached to the object. The mounting blocks have suitably shaped surfaces with which the rounded surfaces of the corresponding elements on the scale engage, in order to embody a interlocking fastening of the scale to the object. For this type of interlocking fastening of a scale, it must be assured in an expensive and complicated way that the mounting blocks are securely fastened in a defined location to the object. In particular, fastening these components of the interlocking connection to be embodied with the corresponding elements on the scale cannot be done solely by means of screws; a pin system must be provided in addition. Thus, the arrangement is comparatively expensive and complicated.